40 patients are included to study the minimal requirement of effective dilation diameter of balloon(s) in performing percutaneous transluminal mitral valvotomy (PTMV) to obtain good hemodynamic and long-term follow-up consequences. The patients are divided into 2 groups depending on the ratio of effective dilation diameter of balloon(s) (determined by calculating the cross-sectional area of the oval enveloping the one or two balloons and then taking the diameter of the circle with the same area) to mitral annular diameter (determined by 2-dimensional echocardiography) (Balloon-Mitral Anular Ratio, BMAR). BMAR in group 1 may be equal to or greater than 0.80 or 0.90, BMAR in group 2 may be less than 0.80 or 0.90. From the careful analysis, the statistically significant immediate hemodynamic improvement, e.g. the reduction of trans-valvular pressure gradient, left atrial pressure, pulmonary artery systolic pressure, the increase of mitral valve area, can be obtained even BMAR is less than 0.80. However, the increase of stroke volume index after PTMV can only be obtained with the BMAR equal to or greater than 0.80. The long-term improvement, determined by greater increment of exercise duration, is also only obtained if the BMAR equal to or greater than 0.80 at PTMV. Therefore, we conclude that to obtain the adequate and satisfactory immediate hemodynamic and long-term follow-up results of PTMV, the BMAR must exceed 0.80.